Various kinds of apparatus are known whereby patients, the injured, and others whose physiological respiratory activity is insufficient or inadequate, are treated with assisted and/or controlled respiration. These devices, which are generally known as artificial respirators, include, among their essential components or apparatus, a pump system which includes a chamber having an alternately variable volume, and a drive means which produces the required cyclic change in the internal volume of the chamber, generally by means of a mechanism which converts the rotary movement of a motor into a reciprocating rectilinear or arcuate movement.
The direct-acting respirators are one category of such devices, in which the gas mixture blow cyclically into the patient's bronochopulmonary system flows through the variable-volume chamber and the appropriate inlet and outlet valves, the respirator thus actng directly as a pumping means to supply the patient with the gases required for the respiratory function, such gases being complemented if required by therapeutic, anaesthetic or other effects.
The devices coming under this category require careful sterilization between successive periods of utilization of all those parts with which the mixture blown into the patient's respiratory system comes into contact (the internal walls of the variable-volume chamber, which is generally formed by a bellows, valves and pipelines). Since it is clearly impossible to subject the entire apparatus to the treatments of complete sterilization in an autoclave (although such treatments would be highly desirable since they have considerable effect even on encapsulated spores) and because the difficulties are obvious in connection with removing the components, the electric motor etc., sterilization is usually carried out via forced circulation by pumping highly toxic and bactericidal gases, such as formalin vapors, nitrogen, compounds, etc. through the variable-volume chamber, the valves and the pipelines.
These sterilization operations based on a flow of gas must be followed by careful flushing out with neutralizing gaseous active substances, such as ammonia vapors, then air, the strictest asepsis conditions being observed at all times.
These requirements in respect of care of respirators mean that tedious and difficult operations have to be performed, while gases are required which are dangerous to store and handle, and in addition there are long periods of interruption in the operation and availability of the respirator.